…nified timezone retrieval.
* `wp_timezone_string()` retrieves the timezone from current settings as a string. Uses the `timezone_string` option to get a proper timezone if available, otherwise falls back to an offset.
* `wp_timezone()` retrieves the timezone from current settings as a `DateTimeZone` object. Timezone can be based on a PHP timezone string or a `±HH:MM` offset.
Props Rarst, remcotolsma, johnjamesjacoby, rmccue.
Fixes #24730.
git-svn-id: https://develop.svn.wordpress.org/trunk@45853 602fd350-edb4-49c9-b593-d223f7449a82